This study was designed to investigate the effect of different sources of $omega$3 fatty acid in the diet with a similar polyunsaturated/saturated (P/S) fatty acid ratio and $omega$6/$omega$3 fatty acid ratio as well as excess DHA on the plasma fatty acid composition and cholesterol level of rats. Three experimental diets contained 10% (w/w) dietary lipids. The control diet and one treatment diet were corn oil-based diets with different $omega$-3 fatty acid sources: perilla (CO) or fish oil (CF), respectively. In order to examine the effect of excess DHA, the other treatment diet (FO) was a fish oil-based diet with corn oil to supply essential fatty acids at the level of 1.8% (w/w) of the diet. Female Sprague Dawley rats were fed the experimental diets for 2 weeks prior to mating and throughout gestation and lactation. Pups were weaned to the same diet of dams at 21 days of age. Plasma fatty acid compositions and cholesterol contents were analyzed for pups at 3th, 7th and 10th week after birth. Plasma DHA concentrations increased significantly as the level of fish oil supplementation increased. Three-, seven- and ten-week old rats fed on CO diet which contained only $alpha$-lino1enic acid as a $omega$-3 fatty acid Source had Plasma DHA levels of 4.85%, 3.15% ana 2.47%, respectively, suggesting that rats at this period of development can convert $alpha$-linolenic acid to DHA. But the ability to form DHA might be limited, since dietary DHA showed to be more effective in raising the plasma level of DHA. There was a significant negative correlation between DHA and cholesterol concentration of the rat plasma at 7th week (r=0.34, p<0.05) and l0th week after birth (r=036, p<0.05), proving the hypocholesterolemic effect of DHA.